Oxidation of polyethers



United States Patent 3,088,970 gPatented May 7, I963 3,088,970 OXIDATIONOF PfiLYETHERS Howard R. Guest, Charleston, and Ben W. Kid, Ona,

W. Va., assignors to Union Carbide Corporation, a corporation of NewYork No Drawing. Filed Mar. 6, 1961, Ser. No. 93,339 8 Claims. (Cl.260-496) This invention relates to a novel process for the oxidation ofglycol ethers to obtain formate and acetate esters. In another aspect,this invention relates to a novel process for the production of glycolsby the oxidation of high molecular weight ethers to obtain estersfollowed by the hydrolysis of the esters to yield ethylene glycol,propylene glycol, diethylene glycol or dipropylene glycol. The glycolethers which can be oxidized by the novel process of this invention canbe represented by the general formula:

R (CHRCH O) H HO (dlHGHzOhH C3H O ((JHCHaOhH i 0511130 (CHCH)4H HO(CH2CH20)4H 021150 (CH2CHzOMH CH3 HO (HCHzOh l-IO (CH2CH2)100 OeHir 020) 15011 0311 0 (CHzOHzDhrw CH3 HO JHOHzO) souH HO (GHzCHzOMoH Theglycol ethers referred to above are well know in the art and can beeasily obtained. However, a particular advantage of our novel process iswhen the starting glycol ethers are obtained as by-products fromethylene oxide and propylene oxide reactions.

Both ethylene oxide and propylene oxide are very valuable compounds andare used to prepare many commercially important derivatives. Among thesederivatives are the mono-alkyl ethers of ethylene glycol and propyleneglycol which are well known in the art as effective solvents for use inpaint and plastics mdustries. Illustrative of these mono-alkyl ethersare the monoethyl, mono-methyl and mono-butyl ethers of ethylene glycoland propylene glycol. These ethers are prepared by the addition ofethylene oxide or propylene ox de to appropriate alcohols under wellrecognized conditions. Other derivatives of ethylene oxide and propyleneoxide are the polyethylene oxides and polypropylene oxides. Thesederivatives are also well known in the art and are manufactured in largeamounts in the chemical industry. In the manufacture of thesederivatives there is also obtained a large percentage of glycol ethersas by-products,

The glycol ethers obtained usually have little commercial importance andthus increase the operating cost for producing the desired derivatives.

It has now been found that when these glycol ether by-products areoxidized in the liquid phase in the presence of an oxygen-containing gasand particular metallic catalysts, surprisingly, they can be convertedpredominately into simple formate or acetate esters. The esters whichcan be obtained by the novel process of this invention are predominatelyethylene glycol diformate, ethylene glycol monofiorrnate, diethyleneglycol monoformate and mixtures of the acetate and formate esters ofpropylene glycol and diproplene glycol. These esters are well known inthe art and have commercial applications as solvents in variousprocesses. The reason why oxidation of certain glycol ethers yieldspredominately acetate and formate esters is not completely understood.However, the fact remains that the long carbon chain is disrupted insome manner to yield the simple esters mentioned above.

The process of our invention is carried out by introducing anoxygen-containing gas into a vessel which contains one or more of theglycol ethers. The temperature and pressure is not narrowly critical andcan vary over wide ranges. The preferred range for the temperature isfrom to 200 C. and for the pressure is from 50 to 1000 psi. Theparticularly preferred ranges are from to 200 C. and from 50 to 200 psi.It is to be understood that when pure undiluted oxygen is used as theoxidizing agent more moderate conditions can be employed than when airis used as the oxidizing agent. The catalysts employed in the process ofthe invention are critical. It has been found that the desired resultscan be obtained when the oxidation is carried out in the presence ofheavy metals such as cobalt, manganese, nickel or chromium. These metalscan conveniently be added in the form of their salts such asnaphthanates, acetates, nitrates, phosphates, and 2-ethylhexanoates. Theamount of catalyst employed may vary over wide ranges. The preferredamount is from 1 to 5000 p.p.m. by weight of the metal based on thematerial being oxidized. The particularly preferred amount of catalystis from 100 to 1000 p.p.m.

A preferred way of conducting the oxidation is to charge the material tobe oxidized and the catalyst into a reaction vessel and then heat it tothe desired tempera ture. The oxidizing gas is then gradually added tothe reaction vessel under the specified pressure. Mechanical stirringcan be employed if it is so desired or a reaction vessel can be chosenof suflicient small cross-sectional area so that the agitation caused bythe added oxidizing agent is sufficient without any mechanical stirring.The esters can then be recovered by conventional means such asdistillation.

in another aspect of this invention, the esters resulting from theoxidation of the glycol ethers are not recovered, but water is added tothe reaction vessel and the esters are hydrolyzed to yield predominantlyethylene glycol, propylene glycol, diethylene glycol and dipropyleneglycol.

This novel method of producing free glycols has many potentialadvantages in commercial applications. Thus, it can readily be seen thatone can utilize by-products which have but little commercialsignificance and be able to obtain glycols which are readily salableproducts. 7

Thus, depending on the need of the operator or the infiuence of marketconditions, the novel process of this invention allows for theproduction of either esters or free glycols.

The following examples will illustrate the novel process of thisinvention.

3 EXAMPLE 1 Oxidation of Ethoxy Triethylene Glycol The reactor employedfor the oxidation was a threeinch I.D. stainless steel tube 62 incheslong. The lower 23 inches of the reactor were jacketed with a shellthrough which steam was circulated. The temperature ot the steam wasregulated by passing it through a mixing faucet by means of which watercould be admitted as needed. A cooling coil extended into the reactorthrough the top to allow condensation of vapors in the effluent gas ifdesired.

Temperature measurements were made through a thermowell extending intothe reactor. A sample line entered the wall just above the heatingjacket and extended nearly to the bottom of the reactor. Compressed airWas admitted from a cylinder through a line entering the bottom of thereactor and from there through a diffuser into the liquid. The effiuentgas passed from the reactor through a control valve by means of whichthe pressure on the system was regulated.

To this reactor there was charged a mixture of 4652 grams of ethoxytriethylene glycol and 4.6 grams of cobalt Nuodex solution. (CobaltNuodex is a commercial product which is a solution-of cob-altnaphthenate. The solution contains 6% cobalt by weight calculated as themetal.) Air was passed through this solution at the rate of 264liters/hr. while the pressure on the system was maintained at 150 p.s.i.The temperature was held at 100C. for five hours. When the reactionbegan to diminish the temperature was increased to 135 C. for two hours.During this period the effluent gas contained 4% O2 and C02.

The reaction was concluded and the product was distilled. After removalof the water and acetic acid formed as by-products in the reaction, twobroad fractions were collected. One boiled at 75 C./20 mm. to 102 C./ 10mm. and the other at 102 C./l mm. to 140 C./ mm.

Redistillation of these cuts gave compounds which were identified asethylene glycol diformate and diethylene glycol 'monoformate. Some of anintermediate material was obtained which was found to be ethylene glycolmonoformate; Identification was made by comparison with properties ofauthentic samples of the esters.

Confirmation of the identification was made by the following procedure:the material which was identified as ethylene glycol diformate wasreacted with an excess of methanol in the presence of 0.2%alkanesulfonic acid catalyst. The mixture was refluxed and thedistillate was identified as methyl formate. The distillation wascontinued and after all the volatile material was removed the residuewas found to be ethylene glycol. From the amount of methyl formaterecovered it was calculated that the starting material was ethyleneglycol diformate. The same procedure was followed to confirm theidentification of the other two esters.

From the starting ethoxy triethylene glycol there was obtained a yieldof 29 percent to ethylene glycol diformate, 23 percent to diethylenemonoformate and 9 percent to ethylene glycol monoformate. 'Unreactedethoxy triglycol equivalent to percent of that charged was recovered.The total yield to useful glycol esters was therefore 61 percent with aneificiency of about 72 percent. The product contained about 8.5 percentof highboiling residues. The remainder of the loss of efliciency wasaccounted for by the formation of carbon oxides, water and low-boilingacids and esters.

4- EXAMPLE 2 Oxidation of T riezhylene Glycol To the apparatus describedin Example 1 there was charged 3891 grams of triethylene glycol and 3.8grams of cobalt Nuodex solution. Air was passed through the liquid atthe rate of 254 liters/hr. at 150 p.s.i. and a temperature of 150-160 C.After six hours the reaction was terminated and the product wasdistilled. The compounds made in Example 1 by the oxidation ofethoxytriethylene glycol were also found in the product mixture fromthis reaction. The yields were 25% to ethylene glycol diformate, 32% todiethylene glycol monoformate and 6% to ethylene glycol monoformate.

The total yield to useful products was therefore 63 percent. Of thetriethylene glycol charged, 9.8 percent was recovered unchanged. Theefficiency to total useful products was therefore about 70 percent. Theproduct contained 14.8 percent of high-boiling residues. The remainderof the loss in efliciency was accounted for by the formation of carbonoxides, water, and low-boiling acids and esters.

EXAMPLE 3 Oxidation of Poly-(Propylene Glycol) To the reactor describedin Example 1 there was charged a mixture of 2500 grams of poly(propyleneglycol) with a molecular weight of about 2000 and 5 grams of cobaltacetate. Air was passed through the liquid at the rate of 756 liters/hr.while the temperature was held at 150 C. at a pressure of 150 p.s.i. Thereaction was conducted for three hours.

The volatile material was distilled away from unreacted poly(propyleneglycol). Upon redistillation of this material acetic acid was obtainedas a heads cut and the remainder was found to consist of a mixture ofacetates and formates of propylene glycol and dipropylene glycol. Abouthalf of the poly(propylene glycol) charged was converted to the estermixture.

What is claimed is:

1. A process for preparing esters which comprises heating a glycol ethercorresponding to the formula:

gen and alkyl groups of from 1 through 12 carbon atoms, R is selectedfrom the group consisting of hydrogen and methyl, and n is a positiveinteger from 2 through 300, in

the presence of an oxygen-containing gas at a temperature from to 200C., and at a pressure of 50 to 1000 p.s.i. in contact with a salt of themetal cobalt.

2. The process of claim 1 wherein water is added to the reactionproducts.

3. The process of claim 1 wherein the temperature is from 200 C. and thepressure is from 50-200 p.s.i.

4. The process of claim 1 wherein the glycol ether is triethyleneglycol.

5. The process of claim 1 wherein the glycol ether is polypropyleneglycol.

6. The process of claim 1 wherein the glycol ether is epoxy triethyleneglycol.

7. The process according to claim 1 wherein the salt is cobaltnaphthenate.

8. The process according to claim 1 wherein the salt is cobalt acetate.

No references cited.

1. A PROCESS FOR PREPARING ESTERS WHICH COMPRISES HEATING A GLYCOL ETHERCORRESPONDING TO THE FORMULA: